GL_INVALID_OPERATION from glVertexAttribPointer with no VAO bound in Core Profile

Context

OpenGL Core Profile requires a Vertex Array Object to be bound before any vertex attribute state can be modified. The specification states that calling glVertexAttribPointer or related attribute functions while the default VAO (name 0) is bound generates GL_INVALID_OPERATION. This behavior differs from Compatibility Profile, where the default VAO is valid.

Uncertainty

Implementations vary in how strictly they enforce this rule during context initialization and after context loss recovery. Some drivers may defer the error until a draw call, while others report it immediately at the attribute call. The exact point of validation affects debugging strategies and wrapper-layer error checking.

Questions

1. At what precise stage does the specification require the GL_INVALID_OPERATION to be generated — at the attribute call or at the subsequent draw?
2. Does the error behavior change if the context was created with a debug flag (e.g., GL_CONTEXT_FLAG_DEBUG_BIT) versus a non-debug context?
3. Are there documented driver-specific deviations from the Core Profile requirement for VAO binding before attribute specification?